Propagation mechanism of impulse corona and breakdown in oil

The breakdown mechanism of oil dielectric has not been fully understood. Information on impulse corona and breakdown are particularly meager. Breakdown theories postulated in the past are, in general, based on voltage measurements and are mostly restricted to uniform field conditions and slow-varying voltages. In the nonuniform field, previous results1 obtained with a point-to-plane configuration indicated a difference in streamer formation between the positive and negative polarities. The study, then, was based on corona-current measurements, and the formation mechanism was not completely clear. To study this further, data were obtained simultaneously with high-speed camera, still camera, and photocell, as well as current measuring devices, thus giving a correlated and clear picture of the breakdown process of oil.